1. Field of the Invention
This invention relates to a durable, lightweight lead-acid battery. Significant weight savings can be achieved by using carbon fiber structures to fabricate the grid/current collectors, and by maximizing the surface area-to-volume ratio of the active materials. To promote long-term durability, the interfaces between the grid/current collectors and the active materials are tailored with buffer layers, to ensure adhesion and to minimize increases in electrical resistance that might result from the formation of interfacial phases during cyclic charging and discharging.
2. Description of the Related Art
The low specific energy of lead-acid batteries has limited their use in electric and hybrid-electric vehicle applications and other mobile and portable applications, where the weight of the battery is critical to meeting efficiency goals. Specifically, it has been reported that the 100% theoretical specific energy of lead-acid batteries (167 Whkg−1) is lowered to 65% theoretical (109 Whkg−1) by limited mass utilization, further lowered to 51% theoretical (85 Whkg−1) by acid dilution, further lowered to 39% theoretical (65 Whkg−1) by acid surplus, and further lowered to 20% theoretical (33 Whkg−1) by inactive components. (See J. Garche, Phys. Chem, Chem. Phys (2001) 3 pp. 356-367.) Among these factors, mass utilization (35% reduction) and the weight of inactive components (19% reduction) are the two most significant factors.
It has been recognized that the electrode grids of conventional lead-acid batteries are relatively heavy due to the use of lead and lead alloys which have a density of about 11 g/cm3. Accordingly, alternate lighter electrode grid materials have been proposed for use in lead-acid batteries. For example, U.S. Patent Application Publication Nos. 2004/0191632 and 2004/0002006 proposed a lead-acid battery having a current collector constructed of carbon foam; Gyenge et al. proposed the use of high-surface area reticulated vitreous carbon current collectors (see Journal of Power Sources, 113 (2003) pp. 388-395, and U.S. Pat. No. 7,060,391); Das et al. reported the discharge behavior of electrodeposited lead and lead peroxide onto cylindrical carbon rods (see Journal of Power Sources, 55 (1995) pp. 251-254; and Journal of Power Sources, 89 (2000) pp. 112-116); Viala et al. reported the manufacture of negative composite grid/current collectors using woven graphite, silicon carbide, glass or polypropylene fibers (see Journal of Applied Electrochemistry 15 (1985) pp. 421-429; Materials Chemistry and Physics, 13 (1985) pp. 393-408); Sutula et al. reported the use of alumina and carbon fibers embedded in lead to fabricate grid materials (see Electrochemical Science & Technology, 128, 10 (1981) pp. 2060-2064; Electrochemical Science & Technology, 129, 8 (1982) pp. 1749-1752); and Narasimham et al. electrodeposited lead peroxide onto cylindrical graphite substrates as a precursor for the production of inorganic chemicals (see Journal of Applied Electrochemistry 6 (1976) pp. 397-401).
It has also been recognized (see, for example U.S. Pat. No. 6,699,620) that the grid current collecting structure and active material of the positive plate of a lead-acid battery affect the life and current generating efficiency of a lead-acid battery. The cycling of positive plates leads to corrosion between the interface of the lead peroxide active material and the grid material (typically a lead alloy). The positive plates also expand and contract during the cycling. The combination of expansion, contraction, and corrosion reactions limits the life of the positive plate. After exposure of positive plate to cycling, the lead peroxide active material can separate from the grid resulting in a loss of electrical continuity at the interface between grid and the active material.
Therefore, there is still a need for an electrode for a lead-acid battery that reduces the weight of the battery and that minimizes the loss of electrical continuity at the interface between the grid and the active material.